Grinder for wood pieces, particularly sticks

ABSTRACT

A grinder for wood pieces, such as sticks, which is provided with two press boxes arranged opposite a grinding stone and also provided with two grinding pistons operated by hydraulic presses is provided in accordance with the present invention with an intermediary switch arranged between two limit switches which controls the operation of one of the two grinding pistons. This intermediary switch causes a reversal of the other grinding piston by energizing an electromagnet which operates a hydraulic valve.

United States Patent Ullner Sept. 5, 1972 [S4] GRINDER FOR WOOD PIECES, PARTICULARLY STICKS [72] lnventor: Klaus Ullner, Braunschweig, Germany [73] Assignee: Ming Muhlenbau und Industrie Gmbl-l, Braunschweig, Germany 221 Filed: Aug. 19, [970 21 Appl. No.: 64,948

[30] Foreign Application Priority Data Aug. 23, 1969 Germany..........P 19 42 939.1

[52] US. Cl ..24l/282 [51] Int. Cl [58] Field of Search ..241/34, 282

[56] Reierenees Cited UNITED STATES PATENTS 1,602,211 10/1926 Read ..241/282 X 1,359,016 11/1920 Baker ..241/282 X 1,757,031 5/1930 Whitcomb ..241/282 X 2,588,448 3/1952 Worm, Jr. et a|..........241/282 2,703,206 3/1955 Lyall ..241/34 3,528,618 9/ 1 970 Ullner ..241/282 Primary Examiner-Granville Y. Custer, Jr. Attorney-Singer, Stern & Carlberg 5 7 ABSTRACT A grinder for wood pieces, such as sticks, which is provided with two press boxes arranged opposite a grinding stone and also provided with two grinding pistons operated by hydraulic presses is provided in accordance with the present invention with an intermediary switch arranged between two limit switches which controls the operation of one of the two grinding pistons. This intermediary switch causes a reversal of the other grinding piston by energizing an electromagnet which operates a hydraulic valve.

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INVENTOR.

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sum 2 or 2 INVENTOR Klaus ULLNER GRINDER FOR WOOD PIECES, PARTICULARLY STICKS The invention relates to grinders for wood pieces, particularly sticks, with two press-boxes disposed opposite a grinding stone and with grinding pistons operated by hydraulic presses, and with movable slides arranged between the charging hoppers and the pressboxes, each of which slides after a return stroke of the grinding piston is to be opened for the purpose of a refill and is to be closed again before the operative stroke of the grinding piston, actuating means being arranged on the grinding piston or on members fixed thereto for the control of limit switches, which after the operative stroke of the grinding piston effect its return and thereafter permit opening and closing of the slide.

In such grinders, the danger exists that they reach approximately or exactly at the same time the limit position where the grinding operation has to be interrupted for the refill operation of the press-box. At this moment, the entire load would be taken away from the grinding stone, and therewith a difficulty of regulation would be caused, apart from the fact, that a dead period would occur which amounts to a pure loss.

It is an object of the invention to eliminate this disadvantage by providing an intermediary switch arranged between the two limit switches of one grinding piston, which intermediary switch causes the reversal of the other grinding piston. The respective controlling hydraulic press in each case then continues to operate until it reaches the limit switch. During this time, the other grinding piston returns, its press-box can be filled, and a new working operation commences. During this time, the hydraulic press of the grinding piston now working alone is placed in known manner under increased hydraulic pressure, so that the load on the grinding stone remains approximately the same.

In the case that both grinding pistons actuate their intermediary switch at the same time, switches disposed mechanically parallel to the intermediary switches are arranged electrically one behind the other and the current flowing in this case is conveyed to an interrupterrelay, which prevents the return of the one grinding piston.

The operating cycle is terminated when the grinding piston after the return movement has reached its outermost end position and the slide has been pulled out from between the charging hopper and the press-box. This may take place either manually by means of a press-button impulse, when the filling of the press-box must be undertaken manually or in a controlled manner. It is, however, also possible to permit the filling to take place automatically and to permit the initiation of the new operative cycle by means of a limit switch in the outer position of the slide, in which case a time-delayer may be provided.

The invention will be explained in greater detail on the basis of an embodiment by way of example, which is illustrated in the accompanying drawings, in which:

FIG. 1 is a sectional view of the left-hand half of the grinder taken in a plane at right angles to the axis of the grinding stone, and

FIG. 2 illustrates an electric circuit diagram for the control of the hydraulic presses of the grinder shown in FIG. 1.

Referring to FIG. 1, at both sides of rotating grinding stone 32 mounted on a horizontal shaft 310 are arranged diametrically opposed pressing units having each the same construction, so that only one of these units is illustrated in greater detail. Each unit comprises a press-box 33 having a rectangular cross-section which for the purpose of simple production is assembled from four individual parts, namely two hollow side walls only one of which is shown at 34, a bottom wall 35 and a cover plate 36 which latter is provided with a feed opening 37 and with guide grooves 38 for a feed slide 39. Above the feed opening 37 is arranged a charging hopper 31 which is fixedly attached to the housing 40 of the grinder. The edges of the press-box walls 34, 35 and corner plate 36 facing the grinding stone 32 carry so-called finger plates 42 through the slots of which may pass water and wood pulp, but not pieces of wood. These finger plates 42 are subject to wear and therefore have to be replaceable and are attached to the pressbox walls by screws. The side walls 34 of the press-box are also provided with grooves 43 for guiding the grinding piston 15.

The grinding piston 15 is provided with a hydraulic press 45 which is mounted in an extension 46 of the press-box and is supported in this extension by a transverse horizontal pivot pin 47. The piston rod 11 is loosely connected by a transverse pivot pin 29 with the grinding piston 15.

A further hydraulic press 20 is employed for operating the feed slide 39, while another hydraulic press 41 is used for adjusting the entire pressing unit.

Above the grinding stone 32 are arranged in known manner a number of spray nozzles 44. The housing 40 of the grinder is provided in its upper side and above the grinding stone with a closeable aperture 48 for permitting the introduction of a device used for dressing the grinding stone.

In FIG. 2 the piston of the hydraulic press 45 for the grinding piston 15 is designated by 1 while the hydraulic press 20 for the charging hopper slide is provided with a piston 2. The electrical switches are designated by 3 to 10. The piston l is mounted on a piston rod 11 which carries at its outer end a cani carrier 12 whose cam 13 operates the limit switches 3 and 4 as well as the intermediary switches 5 and 6. The switch 7 is operated by the end 14 of the cam carrier 12. A hydraulic valve 16 is operated by the electromagnets 17 and 18 which actuate the hydraulic valve 16 according to the adjacent symbol cross flow or parallel flow. An electromagnet 19 opens one of the switches 8 toward the center of the drawing. The piston 2 of the hydraulic press 20 is mounted on a piston rod 21 which is connected with the charging hopper slide. The piston rod 21 has mounted thereon a drive member 22 for operating the switch 9. Reference characters 23, 24 and 25 designate electromagnets, 26 designates a hydraulic valve similar to hydraulic valve 16, pushbutton switch.

In addition, the electric conductors are illustrated by thin lines; hydraulic conduits are illustrated by heavy Hines, and mechanical connections are illustrated by double lines. Transverse lines at the end of thin lines indicate electric return conductors; black arrows on the heavy lines indicate the direction of flow of the hydraulic pressure medium; white arrows on double lines indicate the restoring force on the electric switches; and a white semicircle indicates a pressure button. A indicates the end positions of the hydraulic pistons l and 2 remote from the grinding stone 2; and l indicates the end positions of the hydraulic pistons l and 2 closest to the grinding stone. All of the reference characters indicated above appear in the left-hand portion of FIG. 2 and corresponding elements in the right-hand portion of FIG. 2 are provided with the same reference characters with a prime added thereto.

in case of a completely automatic control, the drive members 22 or also other parts connected with the piston rod 21 may actuate the press-button switch 30, so as to gain time for the proper filling of the press box, and perhaps also for performing the filling manually. This possibility is indicated by a dash-dotted line. Not shown, however, is a manual switch which the operator may operate for interrupting this automatic procedure.

In operation of the grinder starting from the conditions illustrated in the right-hand portion of FIG. 2 where the pistons l and 2' are in the A position, switch 4' is the only switch that is closed (which has no immediate effect since switch 10' is open), and both valves 16' and 26' occupy the cross-flow position, thereby maintaining pressure on the l' side of pistons l' and 2', the successive steps occur as follows:

Step 1 Manual or automatic closing of switch 30' establishes an electric circuit from plus through electromagnet 24 to minus thereby shifting valve 26' to parallel flow position. Step 2 Pressure medium is admitted to the A side of piston 2' which begins to move, thereby causing the slide 39 (FIG. 1) to close.

Step 3 When piston 2' reaches its I end position, member 22' closes switch 9', thereby establishing a circuit from plus through switch 9' and electromagnet 18' to minus and thus energizing said electromagnet 18' which leads to Step 4 in which valve 16' is shifted to parallel flow position and switch 8' is closed.

Step 5 Piston 1' begins its work stroke, moving from the A' position towards the l position with the immediate effect that cam 13' releases switches 3' and 4' and thereby causes switch 3 to close and switch 4' to open, thereby energizing electromagnet 23' through the circuit from plus through switch 3 and electromagnet 23' to minus.

Step 6 Switch closes which has no immediate effect since switch 4' is now open.

Step 7 As the work stroke of piston l' proceeds, the cam 13' reaches the point where it closes switchs 5' and 6'.

If at this point of the operation of piston l, the lefthand piston 1 should happen to occupy the position shown in the left-hand portion of FIG. 2, i.e. with the switches 5 and 6 held closed by the cam 13, electric connections would be established simultaneously from plus through switches 6 and 8 and electromagnet 17' to minus and from plus through switches 6' and 8' and electromagnet 17 to minus.

As a consequence both valve 16 and valve 16' would be in cross-flow position and both piston 1 and piston 1 would be reversed (towards A and A, respectively,) and move to remove all pressure on the grinding stone 32 (FIG. 1) which, as explained above, is to be avoided. Such prevention is accomplished through the circuit from plus through switch 5', switch 5 and electromagnet 19 to minus, which causes energization of electromagnet 19, closing of switch 8, energization of electromagnet l7 and switching of valve 16' to cross-flow with resulting reversal of piston 1' (towards A).

Step 8 In the absence of the above contingency involving electromagnet 19 (both pairs of switches 5, 6 and 5', 6' being closed simultaneously), the closing of switches 5', 6' (in Step 7) establishes a circuit from plus through switches 6' and 8' to electromagnet l7 and minus, thus causing electromagnet 17 to switch valve 16 to crossflow, whereby piston l is reversed (towards A) and switch 8 is opened. in this case no circuit is established through both switches 5 and 5' since the switch 5 remains open.

Step 9 Piston l' continues its work stroke, thereby again causing opening of switches S and 6'.

Step 10 Member 14' closes switch 7, thereby causing energization of electromagnet 17' by establishment of a circuit from plus through switch 7' and electromagnet 17' to minus.

Step ll Valve 16' is moved to cross-flow position.

Step l2 Switch 8' is opened, whereby in Step 13 piston 1 is reversed, and in Step 14 switch 7 is again opened.

Step 15 The momentary closing of valves 5' and 6' during the reverse movement of piston 1' has no effect since both switch 5 and switch 8' are then open.

Step 16 Switches 5' and 6' are opened (after the momentary closing),

Step 17 Piston 1' arrives at its A position, switch 3' opens, and switch 4' closes.

Step l8 Electromagnet 25' is energized through the circuit from plus through switches 4' and 10' and electromagnet 25' to minus, causing valve 26' to move to crossflow position.

Step 19 Piston 2 is reversed to open slide 39 (FIG. 1) and switches 9' and 10' are also opened.

Step 20 Piston 2' arrives at its A position and the press-box 34 (FIG. 1) can be refilled.

This completes the cycle.

What I claim is:

l. Grinder for wood pieces, particularly sticks, provided with two press-boxes disposed opposite a grinding stone, and with grinding pistons operated by hydraulic presses and with slides arranged between charging hoppers and said press-boxes and operated by other hydraulic presses of which each slide after a return of the grinding piston is opened for the purpose of refilling and is closed again before the operational step of the grinding piston, electric circuit means including limit switches and an intermediate switch controlling the operation of said presses, the grinding piston having secured thereto operating means for the limit switches which after the operational step of the grinding piston effect its reversal and thereafter cause opening and closing of the slide, said intermediary switch being arranged between each two of said limit switches of one grinding piston, said intermediary switch causing the reversal of the other grinding piston through energization of an electromagnet which operates a hydraulic valve.

2. Grinder according to claim 1, including switches arranged mechanically parallel to said intermediary switches, said first-mentioned switches being disposed electrically in series in a circuit which also includes an electromagnet adapted, when energized over said firstmentioned switches, to open another switch in the circuit closed by said intermediary switch and thereby effecting reversal of one of said pistons.

3. Grinder according to claim 1, in which the hydraulic press for the charge hopper slide has a piston rod with a member fixed thereto which in the end position of the opened slide actuates a starting button for the grinder.

4. Grinder according to claim 1, in which the hydraulic press for the charge hopper slide has a piston rod with a member fixed thereto which in the end position of the opened slide causes delayed actuation of a starting button for the grinder.

t 1 i 1F i 

1. Grinder for wood pieces, particularly sticks, provided with two press-boxes disposed opposite a grinding stone, and with grinding pistons operated by hydraulic presses and with slides arranged between charging hoppers and said press-boxes and operated by other hydraulic presses of which each slide after a return of the grinding piston is opened for the purpose of refilling and is closed again before the operational step of the grinding piston, electric circuit means including limit switches and an intermediate switch controlling the operation of said presses, the grinding piston having secured thereto operating means for the limit switches which after the operational step of the grinding piston effect its reversal and thereafter cause opening and closing of the slide, said intermediary switch being arranged between each two of said limit switches of one grinding piston, said intermediary switch causing the reversal of the other grinding piston through energization of an electromagnet which operates a hydraulic valve.
 2. Grinder according to claim 1, including switches arranged mechanically parallel to said intermediary switches, said first-mentioned switches being disposed electrically in series in a circuit which also includes an electromagnet adapted, when energized over said first-mentioned switches, to open another switch in the circuit closed by said intermediary switch and thereby effecting reversal of one of said pistons.
 3. Grinder according to claim 1, in which the hydraulic press for the charge hopper slide has a piston rod with a member fixed thereto which in the end position of the opened slide actuates a starting button for the grinder.
 4. Grinder according to claim 1, in which the hydraulic press for the charge hopper slide has a piston rod with a member fixed thereto which in the end position of the opened slide causes delayed actuation of a starting button for the grinder. 